Metallic-based pedicle rod and screw systems are often used in spinal surgeries to correct spinal deformities and intervertebral disc degeneration. Although these systems have been shown to be useful, there has nonetheless been documentation of a number of clinical problems with these systems. First, there are reports of pedicle screw loosening due to a material stiffness that is significantly higher than that of bone. There are reports of reduced postoperative visualization due to artifacts incurred with radio-imaging of the metallic components. Low interbody fusion rates are thought to be due to excessive load transfer through the posterior column, again due to a material stiffness that is significantly higher than that of bone. Lastly, adjacent level hypermotion, excessive loading and physiological breakdown are also thought to be due to the use of metallic rods.
In response to these issues, spinal device companies have recently launched polyetheretherketone (PEEK) polymer rod systems in an attempt to minimize the imaging scatter associated with metallic implants and to increase anterior load sharing at the operative level. Spinal companies have also developed posterior pedicle-based motion systems in attempt to address these clinical problems as well.
U.S. Pat. No. 4,743,260 discloses polymeric pedicle rods, and teaches the use of polymers with carbon fiber reinforcements to enhance strength. In addition, a 1995 thesis compiled by Balli at the University of Akron specifically discloses the use of chopped carbon fiber reinforced PEEK for pedicle-based spinal fixation systems.
PCT Patent Publication WO2006/118866 (Trieu) discloses composite components for use in spinal fixation systems, wherein the composite components comprise polyetheretherketone (PEEK) or another non-resorbable or resorbable polymeric material and at least one metal. Incorporation of PEEK or another non-resorbable or resorbable polymeric material into the components allows average or mean physical properties (e.g., tensile strength, modulus of elasticity, etc.) of the components to be modulated. The composition and orientation of the composite components can be advantageously chosen to produce components with desired physical characteristics.
US Published Patent Application 2006/0229607 (Brumfield) discloses a system, kit and method for treatment of the spinal column, including a plurality of elongate support elements configured for placement across multiple levels of the spinal column wherein at least one of the elongate support elements is formed of a first material and at least one other of the elongate support elements is formed of a second material different from the first material, with the first material having a modulus of elasticity that is different from that of the second material. A plurality of fixation elements are provided which are configured to engage a number of the elongate support elements to the spinal column and which are formed of a third material that is bio-compatible with each of the first and second materials. Further disclosed is an operative kit with elongate support elements (Pedicle rods) with two or more materials, i.e. a kit having metallic and polymeric rods.
Other patents and published patent applications related to this subject matter include: US 2004/0225289 (Biedermann I); US2005/0154390 (Biedermann II); European patent Publication 1579816 (Biedermann III); US 2005/0143823 (Boyd); US2005/0182409 (Callahan); US 2004/0236329 (Panjabi I); US 2005/0222569 (Panjabi II); US 2004/0236327 (Paul I); US 2004/0236328 (Paul II); US2005/0171543 (Timm I); US 2005/0182401 (Timm II); US 2005/0177164 (Walters); and US 2005/0182400 (White).